1. Field of the Invention
The present invention relates to a conveyor and, more specifically, to a belt conveyor for conveying individual articles, such as printed circuit boards.
2. Description of the Prior Art
A conveyor incorporated into a production line for mounting electronic parts on printed circuit boards (hereinafter abbreviated as "PCBs") supports each PCB at the opposite side edge regions of the same with belts to enable electronic parts to be mounted on both of the upper and lower sides of the PCB and to obviate the interference of the belts with the leads of the electronic parts mounted on the PCB.
FIG. 1 shows a conventional conveyor for such a purpose. Referring to FIG. 1, this conventional conveyor has a pair of parallel conveyor rails 1 (only one of them is shown) spaced apart a predetermined distance and provided in their upper surfaces with threaded holes 2 arranged at predetermined intervals. A side rail 5 is fixed to the upper surface of each conveyor rail 1 by inserting bolts 6 through holes formed in the side rail 5 and screwing the bolts 6 in the threaded holes 2. The side rail 5 is provided with a narrow groove 4 in its inner side surface so as to guide the lower surface, the outer side edge and an outer portion of the upper surface of a belt 3 extended between pulleys (not shown) disposed respectively, at the opposite ends of the conveyor rail 1.
FIG. 2 shows another conventional conveyor. Referring to FIG. 2, this conventional conveyor has a pair of conveyor rails 7 each provided integrally with an inward projection 8 from located at the upper end of the same. The inner portion of the upper surface of each projection 8 is recessed to form a step 8a so that a belt 3 is seated on the step 8a with its outer edge and lower surface in contact with the surfaces of the step 8a. A side rail 9 is fixed to the upper end of each guide rail 7, by screwing bolts 10 through holes formed in the side rail 9 in threaded holes 11 formed in the upper surface of the guide rail 7, so as to be in contact with the outer portion of the upper surface of the belt 3 to guide the belt 3.
The belts 3 are guided by the conveyor rails 1 (7) and the side rails 5 (9) to convey workpieces W, i.e., PCBs, supported on the inner portions of the belts 3. However, these conventional conveyors have the following disadvantages.
The arrangement of the conveyor sometimes needs to be changed to deal with a change in the type of workpiece to be conveyed, such as PCBs, or a modification of the production line. In those cases, the position of the side rails 5 (9) on the conveyor rails 1 (7), and the respective positions of the pulleys must be changed. However, such changes cannot easily be achieved and require much time, so that the operation rate of the associated production line is reduced and the changes inevitably involve high costs.